Hashes (also known as “associative arrays”, “maps”, or “dictionaries”) are one of Perl’s three fundamental data structures, and its least understood one. This page gives some resources for learning about hashes.

References allow the programmer to store an aggregate data structure in a simple variable, which can be passed around more easily, to represent complex, nested data structures, and also serve as the basis of Perl's object system.

Scoping is Perl's way of making sure variables are localised and don't interfere with variables of the same name in different places (or alternatively, are not confused with different variables of similar names).

CPAN is the Comprehensive Perl Archive Network, which contains a wealth of open-source and reusable source code, that can be used in your applications. Follow the link to learn how to effectively use CPAN.